1. Field of Invention
The present invention relates to plasma processing and more particularly to monitoring of the plasma processing using an optical system.
2. Description of Background Information
Typically, plasma is a collection of species, some of which are gaseous and some of which are charged. Plasmas are useful in certain processing systems for a wide variety of applications. For example, plasma processing systems are of considerable use in material processing and in the manufacture and processing of semiconductors, integrated circuits, displays and other electronic devices, both for etching and layer deposition on substrates, such as, for example, semiconductor wafers.
Optical diagnostic methods are widely used to monitor plasma processes and to determine an end point of a plasma process, for example, a plasma etching process.
Generally, conventional optical diagnostic methods use a light transmissive window to separate the plasma process chamber from the optical detection system, as the plasma process chamber must operate at low vacuum, typically a few milliTorr to a few Torr. The window tends to become coated with etch by-products that cloud the window. Although this method is widely used and has been quite successful, it is problematic when the window becomes clouded because the optical diagnostic data can be skewed and even can be rendered invalid. In addition, the window would need to be cleaned or else replaced before more product can be processed, either being an expensive and time consuming operation.
Accordingly, it would be desirable to monitor contamination of a window or a viewport for optical diagnostic methods and systems used in conventional plasma processing.